This invention relates generally to electronically controlled fuel injected engines and, more particularly, to a control system for controlling the current levels of a fuel injection signal based upon a sudden engine acceleration condition.
Electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of a fuel injection signal received from an electronic controller. These signals include waveforms that are indicative of a desired fuel injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders of the engine. Each injection waveform may consist of a plurality of distinct and/or rate shaped fuel shots delivered to a cylinder during a particular fuel injection event. As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four cycle engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine.
As is known in the art, to precisely control the power and emissions output of an internal combustion engine, it is necessary to control the timing and quantity of fuel injected into the engine""s cylinders. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an injection signal received from an electronic controller. When using hydraulically actuated electronically controlled unit injectors, the injection signal includes generally a two-tier current waveform that includes a pull-in current level and a generally lower hold-in current level. The higher pull-in current is used to quickly open the fuel injector and thereby decrease the response time, that is, the time between the initiation of a fuel injection signal and the time at which fuel actually begins to enter the engine cylinder. Once fuel injection has commenced, a lower level hold-in current can be used to hold the injector open for the remainder of the injection event.
The performance of such fuel injectors during peak or sudden engine acceleration may be inconsistent due to high injector demands during such acceleration periods and the slow response time of the injector. For example, in a hydraulically operated fuel injector system, the rail pressure will increase during an acceleration event because the controller requests such an increase. During a sudden engine acceleration, the normal pull-in current level for the injector and the duration thereof may be inadequate for quickly opening the fuel injector to deliver the increased required amount of fuel to the cylinders in the appropriate period of time to achieve the requested acceleration. This is true because the response of the fuel injector can be slower due to the increased rail pressure requested during the acceleration condition. As a result, during sudden engine acceleration conditions, it is difficult to accurately control and deliver the proper amount of fuel to the fuel injectors during the appropriate period of time. Consequently, the injection events will usually not be consistent and could inconsistently fuel the engine. This results in erratic engine operation during engine acceleration and/or the engine operation does not successfully match the desired injection event.
It is therefore desirable to improve the responsiveness and performance of fuel injectors during sudden engine acceleration events. In general, a higher pull-in current level will decrease the response time of the injector. Increasing the pull-in current to accommodate sudden engine acceleration will therefore decrease the response time of the injector. However, current levels that are too high for too long may result in undesirable consequences such as thermal damage to the electronic circuitry associated with the generation of the fuel injection signals. In addition, when the pull-in current level is held too high for too long, the fuel injector solenoid or other electrical activating device must be able to withstand the higher electrical power levels and the driver circuit electrical components must be able to provide and tolerate the greater heat. Higher current levels for too long of a duration can also create undue stress on the mechanical components of a fuel injector and possibly degrade its repeatability, whereas reengineering the entire system to provide electronic components capable of handling higher electrical power and/or more robust mechanical components will increase the cost of the overall injector control system.
Typically, the level and duration of the pull-in current and the hold-in current are preselected values that provide such currents for a sufficient length of time to facilitate an acceptable fuel injector response under normal engine speed operating conditions. However, these preselected current levels may not be adequate to provide the desired response under sudden engine speed acceleration conditions.
It is known to provide a boost circuit, such as disclosed in the patent U.S. Pat. No. 5,678,521, or other additional circuitry to generate higher voltage levels to facilitate increased electrical current levels to the fuel injection devices during an acceleration event to expedite the opening of the associated fuel injection devices. However, there are a number of drawbacks associated with such a hardware implementation. These drawbacks include additional circuitry required to step up the battery voltage, additional electrical hardware components which increase the overall cost of the electronics, increased physical space required for the additional hardware, a higher hardware failure rate due to the higher temperatures and increased power levels associated therewith, and the increased size of the electronic control module housing this hardware makes engine mounting applications more challenging. Other disadvantages also exist.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, fuel injection signals are controlled based upon sensing a sudden engine acceleration condition. An electronic controller is coupled to appropriate sensors or other signal producing mechanisms for receiving at least one signal indicative of a condition associated with sudden acceleration of the engine. The sensing of a sudden acceleration condition may be achieved by any one of, or a combination of, various ways or values associated with the operation or performance of the engine such as by sensing a change in engine speed or sensing air intake boost pressure or other parameters. When a sudden acceleration condition is determined or recognized, the controller is operative to output a signal to modify the fuel injection signal to appropriately adjust at least one of the pull-in current level, pull-in current duration, and the hold-in current level, to accommodate and meet the desired acceleration injection requirements. The modified fuel injection signal results in improved responsiveness of the fuel injectors during sudden acceleration periods or events. The present method and apparatus is capable of varying the pull-in current level, pull-in current duration, and hold-in current levels as the fuel injector operating conditions transition between normal engine operation and a sudden engine acceleration.